1. Field of the Invention
The present invention relates to a low cost, compact electronic circuit that may be built into the electrical cord of a two wire AC electrical appliance and that implements different levels and schedules of power application based upon control signals provided from either a switch that is remotely located in the appliance and/or a switch that is remotely located at a location on the source side of the electric cord. An alternative implementation is built into a plug-in adapter that connects between a conventional wall outlet and into which a lamp or other appliance may be attached, thereby implementing power level control as determined by the number and timing of on/off switch closures from a remote switch. The invention also encompasses the use of internal electrostatic protection diodes in a CMOS based integrated circuit to power that circuit, thereby producing a minimal-parts-count circuit.
2. Background of the Invention
For AC electrical appliances such as curling irons, heaters, or electric blankets, that incorporate heating elements, a simple two position, ON/OFF switch is commonly used for power control. Such a switch is also common in incandescent lamps, where in the ON position, electrical current is allowed to pass to the lamp, thereby creating full brightness and in the OFF position, no electrical current is allowed to flow to the lamp, thereby turning off the light. A two position, ON/OFF switch, is also used in many electrical loads that incorporate motors. An example is electric fans. If the switch is ON, the fan operates at full speed. If the switch is OFF, no power is delivered to the fan motor and the fan is off.
In many applications, it is desirable to have more than just ON/OFF control. For example, in an electric blanket, it is desirable to have multiple levels of heating in order to adjust for the external air temperature and user preference. In a light, a low lighting level might be desirable to save energy or to set a mood while higher levels would be preferable for reading. For a fan, different fan speeds might be desirable depending upon room size and room temperature.
Different levels of appliance control may often be obtained by modifying the appliance. Many of these alternatives involve a more complicated switch, additional wiring, and/or modifications to the appliance. For example, in the U.S., many lamps are sold that have a so-called three-way socket. Such a lamp socket has three contacts designed to connect to an incandescent light bulb. The outer contact is neutral. There are two inner xe2x80x9chotxe2x80x9d contacts. A three-way switch is provided on the socket. In the first position it supplies power to one of the hot contacts, in the second position it supplies power to the second of the hot contacts. In the third position it supplies power to both hot contacts. In a fourth position it is off and no power is applied to the bulb. A special xe2x80x9cthree wayxe2x80x9d bulb that is commercially available may then be used with the three-way socket to achieve multiple levels of lighting. A three-way bulb has two hot contacts with filaments connecting between each of these hot contacts to a third contact, the xe2x80x9cneutralxe2x80x9d, which is typically connected to the outer ring on the incandescent bulb. Depending upon which hot contacts are energized, either, both or neither of the filaments within the three-way bulb may be energized, consequently providing differing levels of lighting. The problem with this approach to multi-level lighting is that only three levels of brightness are typically provided, the socket is special and must be built into the lamp, and special three way bulbs must be purchased and these are expensive relative to conventional incandescent bulbs.
In a fan, speed control may be obtained by having multiple windings on the fan motor coils and by a multiple position switch, switching between different windings to vary the motor field and thereby vary the fan speed. A multiple position switch is more complicated than a two position switch and a motor that has multiple windings to implement multiple speeds is more complicated than a simple motor having a single set of magnetic field windings or an internally connected field.
There are commercially available lamp dimmers that provide a variable appliance control and that can be installed as a retrofit. These are often sold as a plug-in wall module, into which the consumer plugs an incandescent lamp or other appliance. A potentiometer (which is a type of switch that gives a range of resistance values depending upon its mechanical position) in the dimmer module allows the user to control the power level over a wide range. Power control is then achieved by the phase control of a thyristor, a type of solid state electronic AC switch that turns on in response to a voltage applied at the so-called gate terminal.
Thyristors have the advantage that they are latching. That is, once turned on or fired, even in the absence of additional gate excitation, a thyristor will continue to conduct electrical current until the current flow through the device reduces to zero. A type of thyristor called a triac may be used for a bidirectional AC switch and has three terminals: MT1, MT2 and gate. The MT1 and MT2 terminals act as the two terminals of an AC switch. The voltage signal applied to the gate of a triac, the so-called gate pulse, may be classified according to one of four possible operating modes: quadrant I, II, III, or IV. When the gate pulse is in-phase with the AC line, then the triac is said to use quadrant I operation for positive going current flow (gate pulse is positive and current flows from MT2 to MT1) and quadrant III operation for negative going current flow (gate pulse is negative and current flows from MT1 to MT2). In quadrant II operation, the gate pulse is negative for positive current flow and in quadrant IV, the gate pulse is positive for negative current flow. Although any of the four quadrant operations may be used to fire a thyristor, quadrant I,II and III operation is much preferred because it takes substantially less electrical current to obtain a reliable triggering. Quadrant IV operation requires much higher gate currents to trigger the thyristor.
The disadvantage to potentiometer based dimmers is that they are often not convenient to control because a potentiometer that is mounted in the module at the wall outlet may not be easily accessible. Other products are designed to attach midway in the electrical cord, allowing the consumer to more easily control power levels but also requiring the user to make a more extensive (and permanent) modification to the cord. By contrast, the present invention does not require the introduction of additional switches into the lighting control but uses the existing switches. Furthermore, it can be built into a cordset at the manufacturing point, or it can be added at a later date as a module type of device that is portable among multiple appliances.
U.S. Pat. No. 3,979,601 to Franklin discloses a combination dimmer and timer switch mechanism which connects to the AC line and which implements appliance dimming in accordance with a predetermined timing sequence. A phase-controlled thyrister is used to regulate the appliance power. This system is fundamentally designed to be an open loop system without requiring user feedback for control and utilizes a complicated mechanical switch.
U.S. Pat. No. 4,276,486 to Ahuja et al. discloses a two terminal power controller whereby momentary interruptions of the AC supply are used to signal building lights to change state (if on, to turn off, if off, to turn on). The intent is to allow both a distributed control where each light may be individually turned on, or a global control where all lights may be turned on or off.
U.S. Pat. No. 4,504,778 to Evans discloses a self-powered electronic control system wherein the control circuitry is powered directly off the AC line and wherein momentary power loss events are sensed and are used as inputs to the control scheme. In this system, the voltage drop across the switching device is used to provide power to the control circuitry. This is known as parasitic power. There are problems with using parasitic power. One problem is that the switching device can never be put into a fully on condition but must remain off for a portion of each half cycle so as to supply power to the control circuitry. This can result in undesirable electrical noise imposed upon the AC power line because of the required phase delay. A second disadvantage with parasitically powered devices is that because the entire control circuit is attached in electrical series with the load, a relatively complicated control circuit is required to distinguish between the positive half cycle and the negative half cycle of the AC power as applied to the load. A parasitically powered controller that is series connected with the load cannot distinguish between a switch at the load and a switch at the source. This limits the ability to implement multiple control schemes. Another problem with parasitic power is that the load must be substantially resistive. This is because the control scheme relies upon the voltage and current waveforms being in-phase in order to sense switch closures. A parasitically powered device can only control a thyristor by firing quadrants I and IV. Finally, because the parasitically powered device derives its own power by being electrically in series with the load, it must power the load in order to power itself. This means that when the load is turned off, as through an open switch, power is removed from the controller. Also, this means that the load must have some specific minimum value or else the controller would not receive enough power to operate.
U.S. Pat. No. 4,534,957 to Hollaway discloses a remotely controlled light flasher for an outside building light. This invention describes a control circuit for turning on and off the power to an electrical load with a prescribed timing characteristic.
U.S. Pat. No. 4,695,739 to Pierce discloses a multifunction switch-controlled lamp circuit whereby the number of contact closures of a single pole, single throw switch that occur within a pre-specified time interval are counted and interpreted and then used to control power to a load. The control circuit is parasitically powered and has the problems associated with that design approach.
U.S. Pat. No. 5,030,890 to Johnson discloses a two terminal incandescent lamp controller that is connected in electrical series with a load and a remote switch and that is disposed in a package that is inserted in the base of an Edison style lamp socket. Contact closures at the remote switch are counted and power to a load is controlled at an electronic switching device in response thereto. This control scheme is half cycle parasitically powered and exhibits the problems associated with that design approach. The packaging can present a problem because a user must install the package into the lamp socket and must replace the package with each new bulb. Furthermore, having this package located under a bulb severely limits the ability of the thyristor to dissipate internally generated heat and limits the amperage of the lamp load that can be attached.
U.S. Pat. No. 5,844,759 to Hirsh et al. discloses an electrical shock protection device for appliances that may be built into the plug of an appliance cordset and that may communicate fault or other status information to a remote location over a two-wire power line.
The present invention is of a low cost electronic circuit that may be used to control power levels in an electrical appliance without requiring a special socket, special switches, or modification to the appliance. The invention is powered from a parallel connection to the AC line (no parasitic powering) and is preferably mounted entirely within the plug of an electric cord but may be also be implemented as a plug-in module, as an extension cord, or as a two part system with a control that is distributed between plug and a secondary controller located between plug and appliance. Using this invention, appliance control may be initiated in one of two ways. First, by interrupting the power to the appliance by a momentary toggling of a switch that is external to the appliance, for example a wall outlet that is controlled by a wall switch. Second, by the toggling of a switch located at the appliance. In many cases, this switch could be a simple ON/OFF or single pole, single throw switch, in which case the timing and sequence of switch closures would be interpreted so as to effect a control action. In other cases, the switch could be a more complicated single pole, multiple throw switch, in which case steering diodes would be used to distinguish between different switch settings, allowing the recognition of more complicated control requests. In all cases, the preferred embodiment of this invention is as applied to a two wire appliance where the appliance itself is modified minimally or not at all, but in which existing switches are used to impart information over the power conductors without the requirement for additional control lines.
The present invention can distinguish between the interruption of power at an external switch and the interruption of power at a switch located at the appliance and can react differently to the two events. The advantage of being able to distinguish between two different switch locations is that by having the ability for two different programming schedules, a single product can serve multiple roles. If a wall outlet is controllable from the room wall switch located near the door, then a lamp plugged into that wall outlet can be controlled to be on or off from toggling either the room light switch or by toggling the switch located at the lamp. With the power control device of the present invention, dimming may be implemented in some arbitrary number of steps by on/off control at the lamp and may be implemented using some different number of steps by on/off control at the light switch on the wall. Dimming steps may increase from minimum brightness to maximum brightness when controlled from the wall and may decrease from maximum to minimum when controlled at the lamp or vice versa. Although this example describes the control of dimming levels, the control method might be applied to timed lighting schedules, light level ramping, or light flashing.
The advantage of being able to implement two different control schedules may be illustrated by the situation of a lamp that is equipped with this invention. Suppose the electronic apparatus of this invention is designed so that when the lamp switch is first turned on, the applied power is at the 12% level so that the lamp acts as a night-light. Then when the switch is turned off and on in rapid succession, the lighting level may be increased to 25%, then 50%, and then 100%. Subsequent switch transitions then would not affect power level as long as they occurred relatively rapid and ended in the condition of the lamp switch being closed. The power level would remain at 100%. Whenever the lamp is turned off for a longer period, such as 4 seconds or more, the system resets and the next switch closure results in 12% power and the cycle repeats. Suppose that the electronic apparatus of this invention has also been designed to react differently to switch closures that occur to turn power on or off at the wall outlet to which the lamp is attached. For example, when power is applied from the wall outlet, the lamp has 100% brightness. Then an OFF/ON transition at the switch controlling the wall outlet signals to the lamp controller to reduce brightness to 50%, with subsequent toggling returning the lamp to 100% and then back to 50%. In other words, utilizing conventional on/off switches that are already in existence, two different control schemes may be implemented to control lamp brightness with a single control apparatus.
In the above example, having these two different control schemes might be desirable in a baby""s room. During the night the lamp is adjusted to be at 12% power for use as a night-light. When it is time to change Baby""s diaper, the lighting level may be increased slightly without making the light so bright as to awaken the baby. In an emergency or during daytime use, when having multiple lighting levels may be a nuisance, a wall switch controls the lighting to be full or half power. With multiple lamps attached to the same controllable outlet, global brightness control may be implemented at the wall mounted outlet switch while local brightness control may be implemented at each lamp. If polarity sensitive loads are used, then independent control of two such loads can be achieved using a single controller. This could have value, for example, in the separate power control of the left and right sides of an electric blanket having only two electrical conductors that connect it to a controller. Because two polarity sensitivity loads are used, power level indicators might be added to show the level chosen for each side.
Prior art approaches to implementing a variable appliance power control on an appliance equipped with a two-position ON/OFF switch had the following disadvantages:
i) require retrofit to the existing appliance cord;
ii) require a direct connection to a manual switch;
iii) obtain controller power parasitically (across a thyristor); and/or
iv) are entirely disposed within a lamp socket or within a wall switch.
In contrast, the present invention has the following objects and advantages:
a. Lamp dimming may be controlled by using either an existing switch that is on the lamp or by using a remote wall switch, or both;
b. A different control method may be implemented using the wall switch as opposed to using a lamp switch with a single controller able to recognize the source of control and able to respond accordingly;
c. It receives AC power directly from the AC source and does not rely upon the voltage drop across the switching device;
d. It may be disposed entirely within the plug on an appliance cordset;
e. It may be disposed entirely within a plug-in module into which an AC appliance may be inserted;
f. It lends itself to low EMI switching methods and can deliver near full power to the load;
g. It may be implemented at very low cost, thereby encouraging its widespread adoption;
h. All manual switches and controls are external to the device so that the device has no moving parts;
i. It requires only 3 external connections to implement a full system, namely: source, common and load; and
j. It allows the independent control on a half cycle basis of two separate polarity sensitive loads using a single controller, with each polarity sensitive load being controllable at either the source or at the load.
Further objects and advantages of the present invention will become apparent from a consideration of the drawings and ensuing description.
A power level controller and method for an AC electrical appliance that can be implemented in the plug of the appliance, controlling power in response to switch closures on the appliance and/or remotely located switches that control via a switch controllable power outlet, or alternatively, may be implemented as a module into which an existing appliance is inserted, thereby providing a retrofit solution for appliance control. By using multifunction switches having steering diodes, multiple commands can be transmitted to the controller, all without the need for additional control wires, since all commands are superimposed on the two conductors that deliver power to the appliance. In addition, the independent control of two polarity sensitivity loads may be carried out. With implementations using integrated circuits, the internal electrostatic discharge diodes may be used for the power supply to yield a very low parts count system with minimal wiring between control element and load.